Embodiments of the present invention relates to a polymer composition which absorbs infrared radiation (IR), containing a transparent thermoplastic plastic, an inorganic infrared absorber, also referred to as IR absorber hereinbelow, at least one inorganic nano-scale pigment, and the combination of at least two organic colouring agents of a specific structure, and to the preparation and use of the polymer compositions according to the invention and to products produced therefrom.
In particular, embodiments of the present invention relates to compositions which have high stability—in particular also high colour stability—to weathering both in the visible range and in the IR range.
Embodiments of the present invention relates further to the use of the polymer composition according to the invention containing such IR absorber and colouring agent combinations in the production of glazing for use in buildings, motor vehicles and railway vehicles or aircraft.
Glazing made from compositions containing transparent thermoplastic polymers such as, for example, polycarbonate offer many advantages over conventional glazing made of glass for use in the automotive sector and for buildings. Such advantages include, for example, increased break resistance and/or weight saving, which in the case of automotive glazing permit greater safety for the occupants in the event of road traffic accidents and a lower fuel consumption. Finally, transparent materials containing transparent thermoplastic polymers permit substantially greater freedom in terms of design because they are easier to mould.
It is a disadvantage, however, that the high heat transmissibility (i.e. transmissibility for IR radiation) of transparent thermoplastic polymers leads to undesirable heating of the inside of motor vehicles and buildings under the action of the sun. The raised temperatures on the inside reduce the comfort for the occupants or residents and can involve increased demands in terms of air conditioning, which in turn increase the energy consumption and thus eliminate the positive effects again. In order nevertheless to meet the demand for low energy consumption coupled with a high degree of comfort for the occupants, glazing provided with appropriate heat protection is required. This is true for the automotive sector in particular.
As has long been known, the largest part of solar energy, apart from the visible range of light between 400 nm and 750 nm, is accounted for by the IR range between 750 nm and 2500 nm. Penetrating solar radiation is absorbed inside a car, for example, and emitted as long-wave heat radiation having a wavelength of from 5 μm to 15 μm. Because conventional glazing materials—in particular thermoplastic polymers that are transparent in the visible range—are not transparent in that range, the heat radiation is unable to radiate to the outside. A greenhouse effect is obtained and the interior heats up. In order to keep this effect to a minimum, the transmission of the glazing in the IR should therefore be minimised as far as possible. Conventional transparent thermoplastic polymers such as, for example, polycarbonate are, however, transparent both in the visible range and in the IR.
Additives, for example, which exhibit as low a transparency as possible in the IR without adversely affecting the transparency in the visible range of the spectrum are therefore required.
Of the transparent thermoplastic plastics, polymers based on polycarbonate and polymethyl methacrylate (PMMA) are particularly suitable for use as a glazing material. Because of its high strength, polycarbonate in particular has a very good property profile for such uses.
In order to impart infrared-absorbing properties to these plastics, corresponding infrared absorbers are therefore used as additives. IR absorber systems which have a broad absorption spectrum in the IR range (infrared, 750 nm-2500 nm) while at the same time having low absorption in the visible range (low inherent colour) are of particular interest for that purpose. The corresponding polymer compositions should additionally have high heat stability as well as excellent light stability.
A large number of IR absorbers based on organic or inorganic materials which can be used in transparent thermoplastics are known.
IR-absorbing additives based on organic materials frequently have the disadvantage, however, that they exhibit poor stability towards thermal stress or radiation. Accordingly, many of these additives do not have sufficient heat stability to be incorporated into transparent thermoplastics because temperatures of up to 350° C. are required for their processing. Moreover, during use, glazing is often exposed for prolonged periods to temperatures of more than 50° C., caused by solar radiation, which can lead to decomposition or degradation of the organic absorbents.
IR-absorbing additives based on inorganic materials are frequently markedly more stable as compared with organic additives. The use of such systems is often also more economical because in most cases they have a markedly more favourable price/performance ratio. Accordingly, materials based on finely divided borides, finely divided tungstates or materials based on antimony-doped tin oxide (ATO) or indium tin oxide (ITO) have proved to be efficient IR absorbers because they have a relatively broad absorption band in the IR range.
However, IR absorbers do not cover the entire IR range—even if they exhibit a broad absorption band in the IR range. Furthermore, they exhibit no or only low absorption in the visible range. In addition, about 50% of the energy introduced into a building or a vehicle through a window is caused by radiation in the visible range of the spectrum (400 nm-750 nm). In addition to IR absorbers, it is therefore necessary also to use other pigments and/or colourants which absorb in the visible range of light in order to ensure a low total energy transmission.
Glazing which is used in the transport or infrastructure sector must additionally have a long service life and must not become brittle during that time. In addition, the colour and transparency, like the IR properties, i.e. the protection against heat radiation, should not change or should change only slightly over the lifetime of the glazing. Furthermore, the glazing must have sufficient scratch resistance.
Because of the very long service life that is required, glass is frequently used as glazing material. Glass is insensitive to UV radiation, has low sensitivity to scratching and does not change the mechanical properties over long periods. Because inorganic oxides, such as, for example, iron oxide, are used as pigments and IR absorbers, the IR and colour properties also remain virtually unchanged over long periods. The use of such pigments in thermoplastic materials is not possible, however, because it leads to clouding and/or degradation of the corresponding matrix.
Because of the above-described advantages of plastics, there is therefore a need for materials which exhibit both the good physical properties of thermoplastics and the high colour and IR stability of correspondingly coloured glass.
In order to improve the service life of thermoplastic materials, it is known to provide them with UV protection and/or scratch-resistant coatings. Moreover, a large number of colouring agents which have high light fastness are known. Inorganic IR absorbers are to be preferred over organic IR absorbers because they have higher stability.
It has been shown, however, that the thermoplastic compositions mentioned in the prior art are only inadequately suitable when extraordinarily high colour and IR stability is required. This is the case, for example, when glass glazing and glazing of thermoplastic material are installed together. It is shown here that the colour and IR stability of glass is superior to that of the thermoplastic material. Colour deviations occur in particular when these materials are installed next to one another.
Relatively new is the requirement that the solar direct transmittance “Direct Solar Energy Transmitted to the inside of a Glazing” (TDS, measured according to ISO 13837) or the solar total transmittance “Total Solar Energy Transmitted to the Inside of a Glazing” (TTS, measured according to ISO 13837) of a glazing must achieve specific values and that those values must not change substantially over the lifetime of a glazing. Such requirements will increasingly be made in future because of climate protection.
The bleaching out of colouring agents not only leads to a change in the colour properties but also results in the occurrence of a higher energy transmission. This in turn means that the required transmission values can no longer be observed. Although a change in the IR range is visually unobtrusive, such a change can likewise lead to a change in the performance data as regards the TDS value or the TTS value. The associated increased heat input into the building or the interior of the vehicle is undesirable because the performance of the air conditioning has to be increased.
It is further necessary to configure the colouring of the moulded body in a neutral colour, because the atmosphere of the interior or the interior fittings is affected by intensely coloured glazing. A colour-neutral grey is generally preferred. In some embodiments, the colouring can be changed to a blue-grey, green-grey, red-grey or yellow-grey.
It must be possible to process the composition at the temperatures conventional for thermoplastics without the colour or the performance data changing markedly during the processing.
Compositions based on polycarbonate containing boride- and/or tungstate-based inorganic IR absorbers have been described in various publications.
WO 2007/008476 A1 discloses moulding compositions which are suitable in particular for spectacles and which contain boride-based IR absorbers and specific carbon blacks; by combining those components, a synergistic effect in respect of the IR-absorbing properties is said to be achieved. However, this application says nothing about the weathering stability and the stability of the colouring agents.
JP 2005-047179, JP 2005344006, JP2006249345, EP 1865027 A1, JP07033969, JP 2008214596 and EP2009057 A1 mention compositions containing boride-based IR absorbers in combination with specific anthraquinone-based colouring agents. However, no stable colouring agent combinations within the scope of the present invention are disclosed.
JP 2006-307172 and JP 2007-169503 describe compositions containing inorganic IR absorbers and various colourants from the group of the anthraquinones, phthalocyanines or perinones, nothing being said about the weathering stability of the colourants or specific colourant combinations.
JP 2008-156386 discloses indanthrene colouring agents in compositions containing IR absorbers.
U.S. Pat. No. 6,476,158 describes covered, i.e. non-transparent, polycarbonate-polyester compositions which have particularly high weathering stability and maintenance of the surface gloss. Transparent compositions as in the present invention are not described, however.
None of the above-mentioned documents describes weathering properties of the compositions, the colouring agent combinations according to the invention or the colour and IR stability, and a solution for the problem underlying the present invention is accordingly not rendered obvious.
In the prior art, many colourants have been described as being particularly fast to light and accordingly also stable. The light fastness (determined at ⅓ standard depth with 1% TiO2 (PS 2% TiO2 according to DIN EN ISO 4892-2; transparent colourations with 0.05% colourant; evaluated with 8-step blue wool scale) of the so-called Macrolex colourants (Lanxess datasheets; Technical Information, Lanxess Deutschland GmbH, Functional Chemicals, High Performance Additives, Colorants, 51369 Leverkusen, Germany) such as, for example, the colourants Macrolex® Blue RR (Solvent Blue 97), Macrolex® Violet 3R (Solvent Violet 36), which are intended for use in polycarbonate, has been categorised as 7-8 (8=maximum value). Nevertheless, it has been shown within the context of the present tests that, in polycarbonate compositions, colourants formally categorised as being fast to light do not exhibit the stability according to the invention on weathering.
In fact, it has been shown that only a very small number of colouring agents of a specific structure is suitable, and only in a very specific limited combination, for achieving the present object. Furthermore, it has been shown that this is possible only in combination with specific inorganic pigments and specific inorganic IR absorbers.
The object was, therefore, to provide a composition based on a thermoplastic material which exhibits a high IR performance in combination with good transmission properties in the visible range and high colour and weathering stability. These characteristic values are to change only slightly over the lifetime.
Furthermore, the composition according to the invention is to exhibit no or only slight haze.
It was a further object of the present invention to provide compositions for the production of multi-layer articles and mouldings.